1. Field of the Invention
This invention relates to a system for cooling a turbine assembly in a gas turbine engine and, more particularly, to a gas cooling system having an additional compressor section as a means to increase the pressure of the coolant.
2. Prior Art
High performance gas turbine engines for use in aircraft and in industrial gas turbine engine operating at ever increasing turbine inlet temperatures in order to meet desired power performance and fuel economy goals. In order to allow for higher turbine inlet temperatures without damaging the turbine assembly two approaches have generally been used. First, high-temperature materials, such as metals and ceramics, have been used in the components of the turbine assembly. Second, the flow of coolant, such as compressed air, has been used to cool the highly stressed turbine components.
Generally, cooling of the turbine assembly, by use of a coolant, is accomplished by such techniques as convection cooling, impingement cooling, film cooling and transpiration cooling. These types of cooling techniques are generally used on the stator vanes, the turbine blades and even the front and rear face of the turbine disks. The compressed air coolant is generally bled or taken from the compressed air which the main compressor produces for introduction into the combustors of the engine. The bled air is then transported to the turbine assembly to be used for cooling.
In film cooling, the coolant is generally into passages in vanes and blades and allowed to exit the vanes and blades through apertures along their outside surfaces In leading edge film cooling the coolant exits the leading edge or the edge of the vane or blade closest to the combustors. The coolant flows along the outside surface of the vane or blade, thus forming an insulating blanket of cooler air between the metal and hot gases from the combustors.
However, a problem arises in presently used cooling systems in that the coolant can be supplied to the turbine assembly without sufficient pressure to provide the flow needed for adequate cooling.
A further problem arises in presently used systems using film cooling in that pressure of the main core of gases must be lowered in the combustors in order to prevent the pressure of the main core of gases from overcoming the pressure of the coolant, preventing proper cooling and thereby damaging the turbine assembly.
A further problem arises in presently used cooling systems in that pressure drops in the main core of gases in the combustors causes fuel inefficiency and energy loss in the engine.